The present invention generally relates to electric heaters and, more particularly, to a heater, such as an electric powered water heater, having over temperature shutoff controls.
Electric powered flow-through water heaters are commonly employed to heat fluid, such as water for use in jetted bathtubs, spas/hot tubs, and other heated water applications by heating water flowing through a hollow vessel. Electric water heaters typically include an electric powered heating element arranged in heat transfer relationship with the water flowing within the vessel. In many conventional flow-through water heating systems, one or more thermostats are thermally coupled to the water flowing in the vessel to sense temperature of the water, and the heating element is generally controlled based on the sensed water temperature so as to maintain a desired water temperature. Examples of water heaters are disclosed in U.S. Pat. Nos. 6,080,973 and 6,555,796, the disclosures of which are hereby incorporated herein by reference.
Conventional electric water heaters employed in jetted bathtubs and spas/hot tubs are generally controlled in response to sensed water temperature to maintain a user selectable water temperature in the heated water tub. In many jetted bathtubs, a maximum user selectable upper temperature limit of about 104° F. is typically established according to industry standards. In addition to controlling the heating element to achieve the user selected water temperature, it is also desirable to insure adequate operation of the water heater to prevent an excessive over temperature condition (i.e., overheating and problems that can arise therefrom). For example, in the event that a failure occurs in the heater controls (e.g., a thermostat), the water temperature may exceed a maximum upper temperature limit. The water heater may quickly overheat and experience an over temperature condition when there is an inadequate amount of water present in the heater vessel. Advanced overheating may also occur when there is inadequate water flow through the heater vessel, such as may be caused by the failure of a water pump or other water flow restriction.
In order to prevent the presence of an excessive over temperature condition, some conventional water heaters are generally equipped with a temperature actuated shutoff device that discontinues power supplied to the heating element when a predetermined upper temperature limit is reached. Conventional temperature-based shutoff devices include a snap disc thermal switch connected in series with the power supply input of the electrically operated heating element. The snap disc thermal switch is designed to switch from a normally closed position to an open position to open circuit the power line supplying electric current to the heating element upon detecting a predetermined upper temperature limit. Spas and hot tubs employing the snap disc thermal switch typically have a manually depressible reset button, and require that a user must depress the reset button to reset the heater in order to allow the heater to be energized following an over temperature shut off condition.
Additionally, some heaters are equipped with a pressure sensor located within the heater vessel to sense pressure or fluid flow within the vessel. The sensed pressure and/or fluid flow is used to determine if inadequate water is passed in thermal communication with the heating element. The requirement of multiple temperature sensors and a pressure sensor adds to the cost and complexity of the heater.
It is therefore desirable to provide for a heater having a shutoff control device that is cost affordable and effectively provides over temperature shut off control of the heater upon experiencing an over temperature condition.